Chimps have long demonstrated many aspects of complex culture, from tool use to hierarchical social structure to waging war.

But now, our closest living relatives have discovered a new element of culture, and one that is often thought to be exclusively human: socially transmitted fashion. Chimpanzees at the Chimfunsi Wildlife Orphanage are hanging blades of grass from their ears, a clear fashion statement with no other discernible purpose. They pluck a blade of grass, fiddle around with it-- presumably to make it look "cooler"-- and then stick it in one ear. The result is strikingly similar to a teenager wearing big hoop earrings for the first time. The earring fad originated with one chimp named Julie, and continued after her death.

Chimps are not the only species to exhibit fads: orcas, too, have been observed making sacrifices for fashion. Recently, the "dead-salmon-carrying-fad" swept through pods of orcas, in which individuals would swim around carrying a dead salmon (and presumably swimming with a bit of a swagger, thinking they looked super hip.)

Humans are undeniably unique; we have swept the world at a scale far beyond that of other species. But it is becoming clearer and clearer that we are not categorically different than other animals; we are merely at one end of a long, blurry spectrum.

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But, according to a study in the journal Animal Cognition, chimpanzee culture now includes something that seems altogether arbitrary: ear accoutrements.
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To figure out if this was really a tradition, and not just chimpanzees sticking grass in their ears at random, van Leeuwen and his colleagues spent a year observing four chimp groups in Chimfunshi Wildlife Orphanage Trust, a sanctuary in Zambia. Only one troop performed the grass-in-ear behavior, although all of the chimps lived in the same grassy territory. There’s no genetic or ecological factors, the scientists believe, that would account for this behavior -- only culture.